The present invention relates to a mirror for use in a microlithography projection exposure apparatus, a projection lens for use in a microlithography projection exposure apparatus, a microlithography projection exposure apparatus, and also a method for correcting a surface form of a mirror.
Microlithography projection exposure apparatuses serve for producing microstructured components using a photolithographic method. In this case, a structure-bearing mask, the so-called reticle, is imaged onto a photosensitive layer with the aid of a projection optical unit. The minimum feature size that can be imaged with the aid of such a projection optical unit is determined by the wavelength of the imaging light used. The smaller the wavelength of the imaging light used, the smaller the structures that can be imaged with the aid of the projection optical unit. Nowadays, imaging light having an operating wavelength of 193 nm or imaging light having an operating wavelength in the extreme ultraviolet (EUV) range, i.e. 5 nm-30 nm, is principally used. When imaging light having a wavelength of 193 nm is used, both refractive optical elements and reflective optical elements are employed within the microlithography projection exposure apparatus. By contrast, when imaging light having a wavelength in the range of 5 nm-30 nm is used, exclusively reflective optical elements (mirrors) are used.
In order to enable a good imaging of the structure-bearing mask onto the photosensitive layer, it is necessary for the imaging aberrations of the projection optical unit to be reduced as far as possible. Therefore, it is necessary to ensure the surface form of, in particular, the mirrors used within the projection optical unit with a high precision.